This project's overall objective is to define the relationship between the controlling effects of light and darkness on the turnover of photoreceptor membranes and those controls endogenously generated by neural or endocrine factors regulating adaptation and sensitivity. Because of their particularly high rate of membrane turnover compound eyes of higher crustaceans provide a particularly favorable preparation for studying the underlying mechanisms. Their similarities and differences relative to man and other vertebrates will aid in the basic understanding of vision. The current year's paticular goal is to follow up the demonstration (Nassel and Waterman, J. Comp. Physiol. 131:205-216, 1979) that the photoreceptor membrane of the rock crab (Grapsus) changes its area by a factor of nearly 20X in going from a maximum state of midnight dark adaptation to the minimum area correlated with noon light adaptation. Major phases of this overall process are the cellular mechanisms and pathways of membrane synthesis which are still largely speculative as well as those for degradation which we have been studying for some time now. Progress requires the application of fresh techniques to the quantitative study of various relevant cytoplasmic organelles including the membrane itself. We want particularly to explore techniques of cell dissociation, scanning electron microscopy and freeze fracture electron microscopy for this purpose. The interaction of external zeitgebers and internal rhythms in controlling adaptation is the major concern.